1 Introduction
IPTV is a broadcast television service that uses IP transmission, also known as broadband digital TV. Utilize the infrastructure of broadband network, use home TV or computer as the main terminal equipment, integrate various technologies such as Internet, multimedia, communication, etc., and provide various interactive programs including digital TV to home users through Internet Protocol (IP). Digital media services. The structure of IPTV is shown in Figure 1. 
Figure 1 system block diagram
As can be seen from the system diagram, the IPTV service is similar to other services, and is generally composed of a front-end service platform, a bearer network, and an end-user system. The front-end business platform includes live TV programs from TV stations, live satellite programs, live programs and self-run programs transmitted by SDH networks, time-shifted programs stored and re-released, and on-demand programs and information from different content providers. service. At the same time, there are Digital Rights Management (DRM) system, Electronic Program Guide (EPG), authentication, authorization, billing and other operational support systems (BOSS), which output the business content to the bearer network through the streaming media system. The bearer network includes an IP backbone or metropolitan area network, a content distribution system (CDN) and copper, two-way HFC, wireless (GSM or CDMA or WLAN) access networks. The end user system may be TV, STB+TV, PC, CM+PC, mobile phone, and the like.
2. Key technologies of IPTV
2.1 video and audio coding
Digitizing video signals is an important part of IPTV content delivery. Video codec technology is one of the key technologies of IPTV. At present, the mainstream video coding technologies in the digitization process are: MPEG-2 (ISO/EC13818-2), MPEG-4Part2 (ISO/IEC14496-2), H.264/AVC (ie MPEG-4 Part 10), AVS, Microsoft WMV. -9, Real's video format. Common standards are MPEG-2, MPEG-4, H.264, AVS. They have their own characteristics.
MPEG-2 is a motion image compression standard whose main purpose is to provide a coding scheme for standard digital television and high definition digital television. The standard is fully compatible with the MPEG-1 standard, and its processing power can reach the broadcast level (ie 720 × 480 pixels), suitable for the encoding range of 1.5 ~ 80Mb / s. The currently known DVD is the format used.
MPEG-4 (Part 2) is an ISO design for real-time images with a transmission rate lower than 64 kb/s. It is an efficient coding standard with an encoding efficiency of 1.4 for MPEG-2. It combines multiple technologies in the fields of digital TV, interactive graphics and the Internet, and greatly improves the coding compression rate, while also improving the flexibility and interactivity of transmission.
H.264, or MPEG-4 AVC, is a video codec developed jointly by ITU-T and ISO/IEC. It is the 10th part of our most familiar MPEG-4 standard (ISOMPEG-4Part10). ). It not only can save MPEG-4 50% code rate, but also introduces an encoding mechanism for IP packets, which is more conducive to packet transmission in the network. H.264 also has high coding efficiency and image quality, which represents the development direction of codec technology.
AVS is the second generation source coding standard with independent intellectual property rights in China. It includes support standards such as system, video, audio, digital rights management and other four major technologies and conformance tests. The coding efficiency is 2 to 3 times higher than that of MPEG-2; it is equivalent to AVC, and the technical solution is simple, and the chip implementation is difficult and difficult: coding efficiency and reconstructed image quality are also equivalent to H.264, and the implementation of CABAC is difficult. Technology, which increases achievability.
2.2 Digital Rights Management (DRM)
Due to the lack of effective protection mechanisms, IPTV development will be hindered and bottlenecked, and its current solution is DRM. DRM technology is a technical means of protecting the copyright of content providers' private videos, music or other videos. It works by: Media producers embed copyright information into media content during the production phase of the program and protect it by encryption. When it is necessary to verify the information of the legitimacy of the media, the copyright information is read out from the media by a technical method or means, so that the copyright information can be compared. DRM is a system concept that includes the use of digital copyright information, the management and distribution of protected digital media content. The DRM currently used is a digital watermark (Digital Watermark). It uses a certain algorithm to write relevant copyright information into certain landmark information of the content to achieve the purpose of proving copyright attribution and tracking infringement.
2.3 multicast technology
IPTV is based on two receiving modes of video streaming: broadcast receiving and on-demand receiving. Different receiving modes have different bearer technologies. Broadcast reception is non-interactive, and multicast requirements are imposed on the bearer technology of the IP network; on-demand reception has the characteristics of real-time interaction, and the IP network bearer technology is required to push the video stream to the user access network. IP multicast sends IP packets from one source to multiple destinations, ie a copy of the information is sent to all recipients of a group of addresses; IP multicast transmits the IP packets to a set of hosts that make up the multicast group, Each member of the group can be distributed on each independent physical network. The relationship between members of the multicast group is dynamic. Members can join or quit at any time. IP multicast can effectively save bandwidth and resources, and facilitate network capacity management and control. The overhead greatly reduces the load on the sending server and reduces the congestion of the backbone network.
2.4 Content Distribution Network (CDN) Technology
The full name of the CDN is ContentDeliveryNetwork, the content distribution network. It is to add a new network architecture to the existing Internet. The purpose is to distribute Internet video and web content to the CDN node close to the user through CDN, so that users can get the required content nearby and improve the user's access to the website. The speed of response. CDN technology combines multi-point load balancing, routing or caching technology, and uses intelligent distribution technology to distribute content to multiple nodes according to the location of the visiting user according to the principle of proximity access. From the user's point of view, the response time is shortened and the stability of data transmission is improved by the CDN system, thereby improving the overall performance of the network service.
The CDN network architecture is mainly divided into two parts: the center and the edge. The center refers to the CDN network management center and the domain name server DNS redirection analysis center. It is responsible for global load balancing. The device system is installed in the management center computer room. The edge mainly refers to the remote node, and the CDN distributes multimedia content. The carrier is mainly composed of a cache server cache and a load balancer. The main technical means to implement CDN is cache and mirror server. It can work in DNS resolution or HTTP redirection, and completes the content transmission and synchronization update through the Cache server or the mirror site in different places. The DNS mode user location judgment accuracy rate is greater than 85%, and the HTTP mode accuracy rate is more than 99%; in general, the ratio of the amount of user access inflow data of each Cache server group to the amount of data fetched by the Cache server to the original website is 2:1. Between 3:1, that is, 50% to 70% of the amount of repeated access data to the original website (mainly pictures, streaming media files, etc.); for mirroring, except for data synchronization traffic, the rest are done locally, not Access the original server.
Advantages of CDN technology: Reduce network bandwidth, access latency, response time, improve network performance and availability of website content; improve control of website resources, intelligently distribute content and perform traffic management; content providers can determine service content locally, The content is dynamic and the content being sent is protected; low-cost content provides improved service content, quality of service and speed of service. CDN has opened up a new way for conducting business and deploying applications on broadband networks, with broad market prospects and long-term profitability.
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2.5 set-top box (STB)
The IPTV set-top box is similar to a digital TV set-top box and has two major components: software and hardware. The hardware of the set-top box is divided into three categories: a dedicated chip-based architecture (SOC+ASIC); based on the multimedia digital signal processor (DSP) architecture, MPEG-2/4 video and audio processing and H.264 video processing can be easily implemented. It also supports other codec standards for IPTV and platforms based on the X86 architecture.
The IPTV set-top box acts as a user-receiving device and connects to the bearer network to convert the received IP data into data that can be displayed on the TV screen. In terms of access support, the STB generally needs to support more LAN or xDSL or WLAN, etc. Broadband access mode, FTTH access support will be provided in the future; in terms of protocol support, STB needs to support TCP/UDP/IP protocol family to complete interoperable information network transmission, and IP data and video streaming media data reception and Processing work; in the decoding support of the received video stream, the standard formats that are generally required to be supported are MPEG-2 MPEG-4, H.264, AVS, WMV, Real, and the like. In addition, STB also supports video on demand, digital rights management, HTML web browsing, content caching, interactive control and business and network management functions.
3. Problems in the development of IPTV
3.1 Technical issues:
(1) Video coding technology: At present, the video coding technologies used in the IPTV service mainly include H.264, MPEG2 and MPEG4. Although these technologies have become international standards, we will face the problem of expensive patent fees if adopted; AVS Although it is an IPTV video coding technology independently researched and developed by China, it has not been listed as an international standard. Some technologies still need further verification and improvement, and many equipment manufacturers are still waiting to see.
(2) Content storage technology: The cost of storage devices accounts for a considerable proportion of the entire IPTV system. At present, operators often use existing local storage devices to meet the needs of IPTV services. However, as the rapid growth of storage content will quickly consume these resources, an effective solution is urgently needed.
(3) Network transmission technology: Existing networks are designed according to their own business characteristics. The IP network of the telecom operator is suitable for the development of interactive services, but has limited support for real-time and one-way high-traffic services. The HFC (Hybrid Fiber Coax) network of the broadcasting and TV system is essentially a one-way network. To achieve interaction, it needs to be modified in both directions. In addition, the bandwidth of the existing network, especially the bandwidth of the metropolitan area network and the access network, cannot meet the large-scale development of multimedia services, and cannot carry a large number of users with high bandwidth requirements, and cannot provide sufficient quality of service guarantee. At the same time, the routing equipment of the existing network generally lacks support for multicast technology. Therefore, it is necessary to re-engineer when developing the IPTV service.
(4) Multimedia terminal technology: At present, the final function and structure of the IPTV terminal have not yet been finalized. The equipment manufacturer does not dare to invest too much capital and manpower for research and development, and it is impossible to form a production scale.
(5) Technical standard issues: Due to the lack of uniform technical standards, the equipment provided by each equipment manufacturer lacks the interoperability in terms of communication protocols and coding formats, and the content between the networks is difficult to transmit smoothly, which will increase network construction and The cost of operations.
3.2 non-technical issues
(1) In the industrial chain, the structure is unclear, the responsibility of the content operators and the regulatory power are not clear, the strength of most links is relatively weak, and the links between the links are waiting to be fulfilled.
(2) In terms of operations, there are problems such as unclear operating mode, unclear operating entities, weak operational network capabilities, insufficient content, lack of operational motivation, and unclear tariff policies.
(3) In terms of policies, there are long-term supervision, market access policies are not clear, transmission security supervision, equipment access and consumer rights protection issues.
4IPTV development strategy
Although IPTV is of great significance for promoting the national economy and social information, promoting the integration of the three networks, and promoting the development of the communication information industry, there are still many obstacles on its way forward. What is going on is the management system of telecommunications and broadcasting and television. And the regulatory power of the radio and television sector. The IPTV market has broad prospects and is favored by all parties. The broadcasting and television use policy has its own right to control access, excludes telecommunications companies, and only allows enterprises within the broadcasting and television system to operate IPTV services. Obviously, it is a huge economic benefit. Under such a management system, on the one hand, telecom enterprises have not fully utilized the modern communication network built by investing huge amounts of funds for decades, and the large-scale network duplication has caused the loss of social wealth; on the other hand, the market The restrictions on access have distorted the allocation of resources, creating new monopolies and restricting the healthy development of IPTV. In this context, if we want to promote the progress of China's IPTV industry, it is necessary to adjust the current development policy.
4.1 Breaking departmental restrictions and promoting triple play
The triple play of telecommunication networks, computer networks and television networks is generally regarded as the future development trend of information technology, and IPTV is the best opportunity to achieve triple play. China has clearly stated in the "10th Five-Year Plan" of the communications industry that it is necessary to expand the use of the Internet and promote the integration of telecommunications, television and computer networks. Up to now, the telecommunication network and the Internet have formed a good fusion architecture. The main problem lies in the integration of telecommunication networks and wide-area networks. Under the influence of the global technology wave, the integration of the three networks is about to usher in substantial progress, which depends on the advent of an opportunity.
The emergence of IPTV will break the original closed state of broadcasting and telecommunications, and promote the integration of telecommunication network and broadcasting network. Through cooperation with TV content providers, telecom operators have broken the monopoly of broadcasting and television from the vertical integration of content production, dissemination and operation. Through competition at all levels, it will inevitably promote the prosperity and development of network TV services. It will help enrich network services and applications, and will also greatly increase the demand for bandwidth while bringing huge economic benefits.
According to the actual situation in China, the management system for film and television and TV program content can be maintained in the short term. However, since the content of IPTV also involves Internet content, a contact conference system between broadcasting, telecommunications and other departments should be established. The communication management issues of IPTV are fully communicated and coordinated. In the long run, a three-network integration regulatory agency should be established to integrate the economic control of different networks such as telecommunications, broadcasting, and the Internet into a unified organization.
4.2 Update concepts, innovate in the cultural industry system and structure, and integrate it with the IPTV industry
Vigorously promoting cultural construction and developing our cultural undertakings and cultural industries are the key tasks of spiritual civilization construction. However, for a long time, we have over-emphasized the cultural ideological attributes and publicity and education functions, ignoring the cultural attributes of culture and consumer entertainment. Function has affected the full play of cultural functions. In the context of the increasingly integrated economy and culture, the development of cultural industries, including modern media industry and digital entertainment industry, is directly realized on the modern communication network platform. At the same time, the development of traditional culture needs to be enhanced by the modern network platform. Attractive and competitive. The content of IPTV dissemination has strong ideological characteristics. Therefore, the development of IPTV is conducive to cultural communication, improving the quality of people's entertainment content, and satisfying the interests of consumers while safeguarding national interests and providing cultural guarantee for creating a harmonious society. . Therefore, it can be said that IPTV is a business that can be profitable and can spread advanced culture. The integration of cultural industry and IPTV business complements each other and can bring a broader development space.
4.3 Introduce positive incentive policies to create a good external development environment
As a combination of broadband network and home TV sets, IPTV is more convenient to operate and more user-friendly. This will further reduce the technical barriers brought by the Internet due to terminal reasons, so that more ordinary people can enjoy the convenience brought by online information. The development of IPTV services has expanded the scope of network grants. Many traditional industries can be moved to the network to enable telemedicine and distance learning. It promoted the government's e-government on the Internet and greatly narrowed the digital divide between urban and rural areas, between the east and the west, between developed regions and underdeveloped regions. IPTV has solved the final access problem of informatization and will greatly improve the level of social information in China. Therefore, governments at all levels should fully recognize the importance of IPTV, introduce positive and positive policies that encourage their development, and create a good external development environment.
4.4 Strengthen market supervision and promote the healthy development of IPTV business
Strengthen market supervision, clarify the responsibility and operation mode of content operators, strengthen network operation capabilities, enrich program content, strengthen supervision over program content monitoring and transmission security, clarify tariff policies, effectively protect consumer rights, and promote IPTV Healthy and orderly development of business.
5 Conclusion
IPTV is a service that realizes video services and triple-play integration on a telecommunication network. It is not only an extension of telecommunications to the broadcasting and television industry, but also an inevitable trend in the development of telecommunications services. IPTV is a new medium that focuses on the needs of users' TV content and provides high-quality and convenient services. It is the sum of personalized interactive TV and Internet TV. Under the main trend of "three-network business integration", consumers welcome interactive services such as IPTV, which will certainly promote the overall prosperity and growth of the entire telecommunications industry.
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